U.S. patent number 7,659,346 [Application Number 11/528,411] was granted by the patent office on 2010-02-09 for process for maleating polymerization residues and products.
This patent grant is currently assigned to Equistar Chemicals, LP. Invention is credited to Jeffrey A. Jones, Chun D. Lee.
United States Patent |
7,659,346 |
Lee , et al. |
February 9, 2010 |
Process for maleating polymerization residues and products
Abstract
A process for converting distillation residues obtained from
polymerization processes to useful maleated products is
provided.
Inventors: |
Lee; Chun D. (Cincinnati,
OH), Jones; Jeffrey A. (Morrow, OH) |
Assignee: |
Equistar Chemicals, LP
(Houston, TX)
|
Family
ID: |
39225866 |
Appl.
No.: |
11/528,411 |
Filed: |
September 27, 2006 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20080076875 A1 |
Mar 27, 2008 |
|
Current U.S.
Class: |
525/242;
525/285 |
Current CPC
Class: |
C08F
6/28 (20130101); C08F 255/02 (20130101); C08F
255/02 (20130101); C08F 222/06 (20130101); C08F
6/28 (20130101); C08L 51/06 (20130101) |
Current International
Class: |
C08L
51/06 (20060101) |
Field of
Search: |
;525/242,285 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Mullis; Jeffrey C
Attorney, Agent or Firm: Baracka; Gerald A. Schuchardt;
Jonathan L.
Claims
We claim:
1. A process for the maleation of a distillation residue containing
4 to 10 weight percent hydrocarbon diluent, 5 to 20 weight percent
polyethylene having a density of 0.940 to 0.955 g/cm.sup.3 and melt
index according to ASTM D 1238-01, condition 190/2.16 of 0.02 to
0.3 g/10 min, 60 to 90 weight percent polyethylene wax having a
number average molecular weight from 100 to 30000 and 0.2 to 1
weight percent catalyst residue, comprising: (a) treating the
distillation residue to remove hydrocarbon diluent; (b)
incorporating 1 to 10 weight percent maleic anhydride, based on the
weight of the distillation residue; (c) incorporating 0.25 to 6
weight percent organic peroxide, based on the weight of the
distillation residue; (d) heating the mixture above the
decomposition temperature of the organic peroxide until the maleic
anhydride is reacted; and (e) recovering the maleated product.
2. The process of claim 1 wherein the hydrocarbon diluent is
hexane.
3. The process of claim 1 wherein (a) is conducted at a temperature
in the range 120.degree. C. to 150.degree. C.
4. The process of claim 1 wherein the residue treated in accordance
with (a) contains less than 200 ppm hydrocarbon.
5. The process of claim 1 wherein the maleic-anhydride
incorporation is carried out in the melt state.
6. The process of claim 5 wherein the amount of maleic anhydride
incorporated is from 1.5 to 8 weight percent.
7. The process of claim 1 wherein the organic peroxide
incorporation is carried out in the melt state at a temperature
below the decomposition temperature of the organic peroxide.
8. The process of claim 7 wherein the amount of the organic
peroxide incorporated is from 0.5 to 5 weight percent.
9. The process of claim 1 wherein (d) is conducted at a temperature
in the range 103.degree. C. to 200.degree. C.
10. The maleated product produced by the process of claim 1 which
contains from 0.5 to 7 weight percent bound maleic anhydride.
11. The maleated product of claim 10 further characterized by
having shear dependent viscosity.
12. A process for the maleation of a distillation residue obtained
from a process for the polymerization of ethylene, said
distillation residue containing 4 to 10 weight percent hydrocarbon
diluent, 5 to 20 weight percent polyethylene having a density of
0.940 to 0.955 g/cm.sup.3 and melt index according to ASTM D
1238-01, condition 190/2.16 of 0.02 to 0.3 g/10 mm, 60 to 90 weight
percent polyethylene waxes having a number average molecular weight
from 100 to 30000 and 0.2 to 1 weight percent catalyst residue,
comprising: (a) heating the distillation residue at a temperature
of 120.degree. C. to 150.degree. C. to remove hydrocarbon diluent;
(b) maintaining the residue obtained from (a) containing less than
200 ppm hydrocarbon diluent in a molten state and incorporating
from 1 to 10 weight percent maleic anhydride; (c) incorporating
0.25 to 6 weight percent organic peroxide into the melt containing
the maleic anhydride from (b) while maintaining the temperature of
said melt below the decomposition temperature of the organic
peroxide; (d) increasing the temperature of the mixture from (c)
above the decomposition temperature of the organic peroxide and
maintaining until the maleic anhydride is reacted; and (e)
recovering the maleated product.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a process for converting distillation
resides obtained from polymerization processes to useful products.
More specifically, the process is directed to the maleation of
distillation residues to produce maleated products characterized by
having viscosities which are shear dependent.
2. Description of the Prior Art
High density polyethylene (HDPE) resins are widely utilized for
film applications such as for grocery sacks, merchandise bags, can
liners and the like. HDPEs are typically produced by copolymerizing
ethylene with a minor amount of a C.sub.3-8 .alpha.-olefin
comonomer using either Ziegler-Natta catalysts or the so-called
Phillips catalysts. The latter are chromium oxide catalysts and
generally produce HDPE resins having broad molecular weight
distributions (MWDs) whereas Ziegler-Natta catalysts, which are
based on transition metal technology, produce narrower MWD
HDPEs.
While most HDPEs exhibit good tensile and stiffness properties,
certain improvements, such as increased tear properties and
increased impact strength, can be achieved by increasing the
molecular weight of the resin. High molecular weight resins are,
however, more difficult to process for film production and require
the use of higher processing temperatures and/or pressures. To
ameliorate this effect, high molecular weight high density
polyethylene (HMW HDPE) film grade resins preferably have broad
MWDs.
Multiple-stage polymerization technologies wherein polymers of
different molecular weights are produced in separate reactors and
blended to produce a final resin product are a known means of
producing resins having broadened MWDs (see e.g., U.S. Pat. No.
5,236,998)
U.S. Pat. No. 4,357,448 discloses a process wherein ethylene or a
mixture of ethylene and a small amount of another .alpha.-olefin
are polymerized in two successive steps under different hydrogen
partial pressures using high activity Ziegler-type catalysts to
produce HDPE resins having broad MWDs. A similar procedure for the
production of high molecular weight medium density polyethylene
resins is disclosed in U.S. Pat. No. 6,770,715.
In one mode of operation for the production of HMW HDPEs where
successive polymerization steps are employed, ethylene is
homopolymerized in a first reactor in a hydrocarbon diluent, such
as hexane or heptane, and the amount of molecular weight regulator,
i.e., hydrogen, is maintained at low levels to maximize molecular
weight of the homopolymer formed. The high molecular weight
homopolymer produced in the first reaction zone is then fed along
with the solvent and catalyst to a second reaction zone where
ethylene and a C.sub.3-8 .alpha.-olefin comonomer are copolymerized
in the presence of the homopolymer. The ratio of homopolymer
produced in the first reactor to copolymer produced in the second
reactor (which typically has a lower molecular weight) is selected
to provide the desired average molecular weight and MWD in the
final resin product for optimal physical properties and processing
characteristics.
While such processes are an effective and versatile means for
producing a broad array of HMW HDPE resins of varying densities and
melt indexes (MIs), substantial amounts of low molecular weight
polymers (LMWPs) are also formed. The LMWPs have number average
molecular weights (M.sub.n) from several hundred up to about 30000
and, more typically, up to about 20000. These low molecular weight
by-product polymers have a waxy character and they remain in the
hydrocarbon diluent after separation and recovery of the HMW HDPE
by centrifugation or other suitable means.
In a typical HMW HDPE operation, the hydrocarbon diluent containing
the LMWP, any unrecovered HMW HDPE and catalyst residue is
subjected to one or more distillations to recover the hydrocarbon
which is recycled for reuse in the polymerization process. The
still "bottoms" obtained from the distillation, also referred to
herein as the polymerizer/polymerization residue or by-product,
generally contain about 60 to 90 weight percent (wt. %) LMWP, 5 to
20 wt. % HMW HDPE, 4 to 10 wt. % hydrocarbon diluent and 0.2 to 1
wt. % catalyst residue and catalyst deactivating agents, e.g.,
alcohols.
Even though the low molecular weight ethylene polymer waxes are the
major constituents, these polymerizer residues cannot be used as
such for most wax applications due to the presence of significant
levels of the high molecular species (which increase the viscosity
to a level outside the useful range for most wax applications) and
their high metals content due to the presence of catalyst residues
(which form undesirable color bodies).
Since separation of the low and high molecular weight species and
removal of catalyst residues is difficult and not economically
feasible, it would be highly desirable if a process were available
whereby the polymerization residues recovered from such processes
could be effectively treated and converted into useful products.
These and other advantages are achieved with the process of the
present invention which is described in detail to follow.
SUMMARY OF THE INVENTION
The invention relates to a process for maleating by-products
recovered from HMW HDPE polymerizations. In addition to converting
by-products to useful products the maleated wax products produced
by the process exhibit unexpected viscosity characteristics.
The process of the invention comprises treating a distillation
residue obtained from a HMW HDPE polymerization processing
containing 4 to 10 weight percent hydrocarbon diluent, 5 to 20
weight percent high molecular weight high density polyethylene, 60
to 90 weight percent low molecular weight polyethylene waxes and
0.2 to 1 weight percent catalyst residue to remove substantially
all of the hydrocarbon diluent incorporating 1 to 10 weight percent
maleic anhydride, based on the weight of the distillation residue;
incorporating 0.25 to 6 weight percent organic peroxide, based on
the weight of the distillation residue; heating the mixture above
the decomposition temperature of the organic peroxide until
substantially all of the maleic anhydride is reacted; and
recovering the maleated product. Products produced by the maleation
process contain from 0.5 to 7 weight percent reacted maleic
anhydride and have a viscosity which is essentially shear
independent.
In a preferred mode of operation, the maleation is conducted by (a)
heating the distillation residue at a temperature of 120.degree. C.
to 150.degree. C. to remove substantially all of the hydrocarbon
diluent; (b) maintaining the essentially hydrocarbon diluent-free
residue obtained from (a) in a molten state and incorporating from
1 to 10 weight percent maleic anhydride; (c) incorporating 0.25 to
6 weight percent organic peroxide into the melt containing the
maleic anhydride from (b) while maintaining the temperature of said
melt below the decomposition temperature of the organic peroxide;
(d) increasing the temperature of the mixture from (c) above the
decomposition temperature of the organic peroxide and maintaining
until substantially all of the maleic anhydride is reacted; and (e)
recovering the maleated product.
DETAILED DESCRIPTION OF THE INVENTION
The present process is directed to a method of utilizing
by-products obtained from processes wherein ethylene is polymerized
using Ziegler-Natta catalysts in a hydrocarbon medium. More
specifically, it relates to a process wherein distillation residues
obtained from multi-stage HMW HDPE polymerizations are maleated to
produce useful products. The by-products treated in accordance with
the process of the invention are comprised of about 60 to 90 wt. %
LMWPs, about 5 to 20 wt. % HMW HDPE, about 4 to 10 wt. %
hydrocarbon diluent and about 0.2 to 1 wt. % catalyst residue.
Catalyst residues include metal complexes, salts, etc., formed
during polymerization or as a result of catalyst deactivation
procedures prior to distillation, e.g., by the addition of alcohols
or ketones to "kill" the catalyst. Octanol is commonly used to
deactivate the catalyst in these types of polymerizations. If this
is the case, the residue may contain up to about 500 ppm residual
octanol. The amount of catalyst residue is determined utilizing
known x-ray fluorescence (XRF) procedures.
The distillation by-products utilized for the process of the
invention are residues obtained from processes wherein a first
ethylene polymer (homopolymer or copolymer) is produced in a first
polymerization zone and a second ethylene-.alpha.-olefin copolymer
resin is produced in a second polymerization zone in the presence
of the first ethylene polymer. The first and second polymers are
produced in the desired ratio to obtain a final HMW HDPE resin
product. The polymerizations are conducted in an inert hydrocarbon
medium in separate reactors connected in series using Ziegler-Natta
catalysts. Polymer produced in the first reactor is fed into the
second reactor with the catalyst, solvent and unreacted ethylene
where comonomer and additional ethylene are added. Such two-stage
processes are known and described in U.S. Pat. No. 4,357,448
details of which are incorporated herein by reference.
Typically, the amount of comonomer present in the first reactor is
very low and, in commercial operations, is the result of the
introduction of recycled gases and hydrocarbon diluent which can
contain comonomer.
The polymerizations are carried out in an inert hydrocarbon medium
using conventional Ziegler-type catalysts. Typically, the same
catalyst is used for both polymerizations; however, this is not
necessary. It may be desirable to add additional catalyst to the
second reactor and this catalyst may be the same or different than
the catalyst employed in the first reactor. Inert hydrocarbons
which can be used for the process include saturated aliphatic
hydrocarbons such as hexane, isohexane, heptane, isobutane and
mixtures thereof. Catalysts are typically metered into the reactors
dispersed in the same hydrocarbon used as the polymerization
medium. Hydrogen may be included in either or both of the reactors
to regulate molecular weight.
In one highly useful mode of operation, higher density, higher MI
polymer, predominantly ethylene homopolymer, is produced in the
first reactor and lower density, lower MI ethylene/butene-1,
ethylene/hexene-1 or ethylene/octene-1 copolymer is produced in the
second reactor. To accomplish this, hydrogen to ethylene mole
ratios from 1 to 10 are employed in the first reactor whereas
hydrogen to ethylene mole ratios from 0.01 to 1 are employed in the
second reactor. When operating in series mode, it may be necessary
to vent hydrogen prior to transferring the first polymer in order
to achieve the desired hydrogen:ethylene ratio in the second
reactor. This can be readily accomplished by means of a flash tank
installed between the two reactors.
MI and density of the first polymer produced in the first reactor
will be in the range 1 to 1000 g/10 min and 0.955 to 0.975
g/cm.sup.3, respectively, whereas MI and density of the second
copolymer produced in the second reactor will be in the range 0.001
to 10 g/10 min and 0.915 to 0.940 g/cm.sup.3, respectively. In a
particularly advantageous embodiment of the invention copolymer
produced in the second reactor will have a density of 0.925 to
0.938 g/cm.sup.3 and MI from 0.01 to 5 g/10 min.
Polymerizations in the first and second reactors are generally
carried out at pressures up to 300 psi and temperatures up to
100.degree. C. Polymerization temperatures are most typically
maintained at 60.degree. C. to 95.degree. C. and, more preferably,
between 65.degree. C. and 85.degree. C. Pressures are most
generally maintained between 80 psi and 200 psi and, more
preferably, from 80 psi to 160 psi when using hexane(s) as the
polymerization medium.
Properties of the final HMW HDPE resin product will vary depending
on the properties of the first polymer and second copolymer
products produced in the respective reactors and the ratio of first
polymer and second copolymer resin components, i.e., composition
ratio. The final HMW HDPE resin will, however, generally have a
density of 0.940 to 0.955 g/cm.sup.3 and MI from 0.01 to 0.5 g/10
min. Densities of the HMW HDPE resins produced by the process are
preferably in the range 0.945 to 0.952 g/cm.sup.3 and MIs are
preferably in the range 0.02 to 0.3 g/10 min. Densities and MIs
referred to herein are determined in accordance with ASTM D 1505
and ASTM D 1238-01, condition 190/2.16, respectively. The HMW HDPE
resins generally have MWDs (M.sub.w/M.sub.n) in the range 20 to
30.
High activity Ziegler-Natta catalyst systems employed for the
polymerizations comprise a solid transition metal-containing
catalyst component and organoaluminum co-catalyst component. The
solid transition metal-containing catalyst component is obtained by
reacting a titanium or vanadium halogen-containing compound with a
reaction product obtained by reacting a Grignard reagent with a
hydropolysiloxane having the formula
.times..times. ##EQU00001## wherein R represents an alkyl, aryl,
aralkyl, alkoxy, or aryloxy group as a monovalent organic group; a
is 0, 1 or 2; b is 1, 2 or 3; and a+b<3) or a silicon compound
containing an organic group and hydroxyl group in the presence or
absence of an aluminum-alkoxide, aluminum alkoxy-halide halide or a
reaction product obtained by reacting the aluminum compound with
water.
Organoaluminum co-catalysts correspond to the general formula
AlR.sup.1.sub.nX.sub.3-n wherein R.sup.1 is a C.sub.1-C.sub.8
hydrocarbon group; X is a halogen or an alkoxy group; and n is 1, 2
or 3. Useful organoaluminum compounds of the above type include
triethylaluminum, tributylaluminum, diethylaluminum chloride,
dibutylaluminum chloride, ethylaluminum sesquichloride,
diethylaluminum hydride, diethylaluminum ethoxide and the like.
High activity catalyst systems of the above types which can be
employed are known and are described in detail in U.S. Pat. No.
4,357,448, which is incorporated herein by reference.
The HMW HDPE polymer is typically recovered from the hydrocarbon
diluent by centrifugation although other means, such as the use of
Zig-Zag separators, may also be employed to separate the polymer
particles from the hydrocarbon medium. Although the bulk of the
high molecular weight resin is recovered, a small amount remains
with the hydrocarbon. Substantial amounts of LMWP formed during the
polymerization are also present in the hydrocarbon diluent as are
catalyst and any modifiers which may have been used for the
polymerization.
The hydrocarbon diluent containing the above components, the
amounts of which will vary depending on the mode of recovery used
and other operational variables, is subsequently distilled to
remove/recover the hydrocarbon which is recycled for use in the
process. Since in the preferred mode of operation, it is customary
to deactivate or "kill" any catalyst present in the hydrocarbon
prior to distillation, e.g., by the addition of alcohols or
ketones, species formed as a result of this procedure as well as
any residual deactivating agent (alcohol or ketone) will also be
present in the hydrocarbon diluent being distilled. Distillation
can be accomplished in a single distillation column but, more
typically, multiple stills are employed. Typically the recovered
hydrocarbon is purified and recycled to the first polymerization
reactor; however, the recycle stream may be split and introduced at
several points in polymerization sequence.
The distillation residue, i.e., the still bottoms remaining when
distillation is complete, are maleated in accordance with the
process of the invention. These residues will typically contain a
small amount of residual hydrocarbon (usually about 4 to 10 wt. %),
some unrecovered HMW HDPE polymer (usually about 5 to 20 wt. %) and
0.2 to 1 wt. % catalyst residue. The latter are various metal
species, i.e., complexes and salts, formed during polymerization
and upon treatment with the deactivating agent. Small amounts of
deactivating agents, typically less than 500 ppm, may also be
present. The bulk of the distillation residue, however, consists of
low molecular weight polymers produced during the polymerization.
These LMWPs, which have molecular weights in the range generally
associated with polyethylene waxes, comprise about 60 to 90 wt. %
of the residue. Molecular weights of the low molecular weight waxy
materials range from about 100 up to about 30000 and, more
typically, are in the range 100 to 20000. Molecular weights
referred to herein are number average molecular weights
(M.sub.n).
The distillation residues are maleated, i.e., reacted with maleic
anhydride, in accordance with the process of the invention to
obtain useful maleated products. The maleated products containing
both low and high molecular weight ethylene polymer species possess
unique viscosity characteristics rendering them useful for a
variety of applications but particularly as
compatibilizing/coupling agents for composites.
For the maleation process, the distillation residue is first
treated to remove substantially all of the remaining hydrocarbon.
This can be conveniently accomplished utilizing known
devolatilization procedures wherein the residue is heated above the
boiling point of the hydrocarbon. Removal of volatiles, i.e., the
hydrocarbon, is generally further facilitated by sweeping an inert
gas over and/or through the product, pulling a vacuum on the system
or by similar means. Commercial evaporators/devolatilizers are
known for these procedures. The temperature used for the
devolatilization will vary depending on the hydrocarbon. When the
hydrocarbon is hexane, widely used as a diluent for polymerization
processes of the type described above to produce HMW HDPE,
temperatures in the range 120.degree. C. to 150.degree. C. will
generally be used for the devolatilization step. Excessive heat
should be avoided to minimize polymer degradation. The devolatized
residue should be substantially hydrocarbon free, i.e., contain
less than about 200 ppm hydrocarbon and, more preferably, less than
50 ppm hydrocarbon.
The substantially hydrocarbon free residue may be stored at this
point or, as is more usually the case, passed directly to the next
step in the process where maleic anhydride is added and
incorporated. Any means suitable to uniformly distribute the maleic
anhydride in the devolatilized residue can be employed. This can be
accomplished in a suitable blender/mixer or in an extruder with a
suitable mixing chamber. The maleic anhydride can be dry blended
with the residue, such as in the case where it has been stored
after devolatilization; however, maleic anhydride incorporation is
preferably carried out in the melt state, i.e., the maleic
anhydride is added to and uniformly mixed into molten devolatized
residue. Temperature of the melt is preferably the same as that
employed for the devolatization step. The amount of maleic
anhydride incorporated will range from 1 to 10 wt. % and, more
preferably, is from 1.5 to 8 wt. %.
After incorporating the maleic anhydride, 0.25 to 6 wt. % and, more
preferably, 0.5 to 5 wt. % of an organic peroxide is added to the
molten mixture. The peroxide is preferably added at a temperature
below its decomposition temperature and this temperature maintained
until the peroxide is uniformly distributed throughout the mixture.
At that point the temperature is raised above the decomposition
temperature of the organic peroxide and maintained until
substantially all of the maleic anhydride is reacted. The maleated
product will contain from 0.5 to 7 wt. % and, more preferably, from
1 to 5 wt. % bound maleic anhydride. The extent of reaction, i.e.,
grafting, is determined using known Fourier transform infrared
spectroscopic (FTIR) techniques.
Organic peroxides and hydroperoxides which decompose at
temperatures below the melting point of the mixture can be used.
Suitable organic peroxides include dicumyl peroxide, dibenzoyl
peroxide, di-t-butyl peroxide, t-butylperoxybenzoate,
2,5-dimethyl-2,5-di(t-butylperoxy)hexane, t-butyl
peroxyneodecanoate, 2,5-dimethyl-2,5-di(t-butylperoxy)hexyne,
t-amyl peroxypivalate, 1,3-bis(t-butylperoxyisopropyl)benzene, and
the like. Hydroperoxides can include di-t-butyl hydroperoxide,
t-butyl hydroperoxide and the like.
The reaction step can conveniently be carried out in the same
equipment used for the devolatilization and/or maleic anhydride
incorporation steps, e.g., using an extruder having a mixing zone
suitable for incorporating the maleic anhydride followed by one or
more reaction zones where maleation can occur. Such extruders would
have suitable screw designs and temperature profiles and be
appropriately configured. Other equipment such as that manufactured
by LIST USA INC. which incorporates a devolatilizer with a kneader
reactor could also be employed to perform all three steps of the
process in one continuous operation.
Temperatures between about 130.degree. C. to 200.degree. C. and,
more preferably, from about 140.degree. C. to 180.degree. C. are
employed for the reaction step. Reaction times will vary depending
on the reaction conditions and the particular organic peroxide
used. Conditions should be such that substantially all of the
maleic anhydride is reacted. For batch operations reaction times
typically range from 3 minutes to 1 hour and, more preferably, from
about 10 to 40 minutes. For continuous operations, such as where
the reaction is carried out in an extruder with highly efficient
mixing and capable of operating at relatively high temperatures,
residence times can vary from 0.5 to 5 minutes.
Maleated products of the invention can be utilized in most
application where functionalized ethylene polymers are been used.
They are, however, particularly advantageous as
compatibilizing/coupling agents for wood-plastic composites (WPCs).
Use of cellulosic-reinforced plastic composites has grown in recent
years as consumers discover the advantages of these products
compared to wood. WPCs are increasingly being utilized for
installations in environments which are unfavorable to the use of
wood, e.g., where cracking, warping, rotting or attack by insects
would typically be expected.
Numerous plastic resins including HDPE, PVC, EVA, ABS and
polystyrene can be used with various cellulosic fillers for the
production of useful WPCs. The amount of cellulosic filler used
will vary depending on the particular resin and filler being used
and the intended application. In general, however, about 40 to 60%
cellulosic filler is utilized for extruded profiles whereas lower
filler loadings, on the order of 20 to 30%, are used for molded
pieces.
The maleated products of the invention are particularly useful for
composites comprised of 35 to 85 wt. % and, more preferably, 40 to
80 wt. % matrix polymer and 15 to 65 wt. % and, more preferably, 20
to 60 wt. % cellulosic filler. The maleated distillation residues
produced in accordance with the process of the invention are
utilized at levels of 0.5 to 20 wt. % and, more preferably, from 1
to 10 wt. % to facilitate processing, incorporation and binding of
cellulosic filler materials.
Useful cellulosic materials can be any of the known products
available from a variety of natural sources or as by-products from
various processes. These can include such diverse materials as
paper, cardboard, wheat pulp, rice hulls, coconut shells, peanut
shells, corn cobs, sawdust, wood chips, wood fiber, wood flakes,
wood flour, ground wood, palm fiber, bamboo fiber, bagasse, jute,
flax and the like. Of these, wood fillers are particularly
useful.
In one highly useful embodiment, the cellulosic filler is a wood
flour. Wood flours are widely available materials produced by
pulverizing various wood residues obtained from commercial
operations, e.g., sawdust, using hammer mills or other suitable
equipment to reduce particle size. Wood flours are typically
classified based on the size of screen mesh through which the
material will pass and 30 to 150 mesh materials are most commonly
used.
In another highly useful embodiment, the matrix polymer is HDPE or
a mixture comprised of a majority of HDPE and one or more other
polyolefins, preferably polyethylene, resins. Reclaim/recycled
resins may also be included in the composites. HDPEs and HDPE
mixtures employed for these applications generally have densities
from 0.940 to 0.970 g/cm.sup.3 and, more preferably, from 0.945 to
0.965 g/cm.sup.3.
To demonstrate the maleation process of the invention, the
following experiment was conducted using a distillation residue
obtained from a commercial two-stage HMW HDPE polymerization
process wherein ethylene-butene-1 copolymer was produced in hexane
using a high activity titanium catalyst and organoaluminum
co-catalyst. As part of the operation, hexane coming off of the
centrifuges used to recover the HMW HDPE was treated with octanol
to deactivate the catalyst and then distilled and purified for
recycle in the process. Residue, i.e., still bottoms, recovered
from this distillation was employed for the example. The solid wax
distillation residue contained 8 wt. % hexane, 0.5 wt. % catalyst
residues, 6 wt. % HMW HDPE and 85.5 wt. % low molecular weight
polyethylene polymers (M.sub.n less than 30,000) and trace amounts
(less than 400 ppm) octanol.
The solid wax residue was transferred to a glass reaction vessel
and heated to 120.degree. C. under a blanket of flowing nitrogen
with stirring (340 rpm) for approximately 30 minutes to remove the
hexane. After completion of this devolatilization step, the amount
of residual hexane was less than 0.01 wt. %.
The temperature of the molten mixture was then increased to
140.degree. C. and 3 wt. % maleic anhydride added while continuing
the stirring. After the maleic anhydride was uniformly dispersed
throughout the molten mixture, 3 wt. % dibenzoyl peroxide was added
and the mixture reacted for 20 minutes at 140.degree. C. with
stirring. After cooling the product was ground.
Analysis of the product by FTIR showed it to contain 1.8 wt. %
bound maleic anhydride and to be substantially free of unreacted
peroxide and unreacted maleic anhydride. The maleated product had a
waxy appearance and two DSC melting peaks (at 82.0.degree. C. and
115.8.degree. C.). The Brookfield viscosity at 150.degree. C. (20
rpm) was 1300 cP.
Additionally, the maleated product obtained from the
above-described procedure exhibited unexpected and highly desirable
viscometric behavior under conditions of shear such as may be
encountered during processing. Whereas typical commercial maleated
waxes exhibit viscosities which are essentially shear independent,
i.e., complex viscosity (P) remains essentially unchanged as the
shear rate (frequency) is varied, the maleated products produced by
the process of the invention using distillation residues containing
both low and high molecular weight polymer species exhibits shear
dependent viscosity.
This is apparent from the dynamic complex viscosity data tabulated
below. The rheological data were determined using a Rheometrics
ARES rheometer at 130.degree. C. in the parallel plate mode (plate
diameter 50 mm). Complex viscosities were determined for a
commercial maleated wax and the maleated product of the invention
in the frequency sweep mode at frequencies (shear rates) ranging
from 2.51 to 398 rad/sec. The commercial wax (EPOLEN C-18P) is a
maleic anhydride-modified low molecular weight polyethylene (Acid
Number 2; M.sub.n 5700; 150.degree. C. Brookfield viscosity 4000
cP).
TABLE-US-00001 Complex Viscosity (P) Maleated Maleated Shear Rate
Product of Invention Commercial Product 2.51 (low shear) 127.3 71.8
10 81.3 68.5 100 31.4 67.2 398 (high shear) 16.3 67
The unexpected difference in viscosity response at varying shear
rates for the two products is apparent from the above data. The
shear dependent viscosity of the maleated product obtained by the
process of the invention renders the product highly useful as a
coupling/compatibilizing agent for the manufacture of wood plastic
composites. Since WPC processes typically are high shear
operations, the lower viscosity of the maleated product of the
invention at high shear renders it readily compatible with the wood
flour filler due to the ease of wettability and facilitates
incorporation in the matrix polymer. The high viscosity at low
shear, which is evidence of molecular entanglements presumably as a
result of the presence of low and high molecular weight polymer
species, imparts enhanced mechanical strength to the finished WPC
product.
* * * * *